This study establishes an evaluation model based on the completeness ratio for the planning and evaluation of watershed management. Using geographic information system, remote sensing, and global position system, soil erosion factors were first estimated to project the annual soil erosion for two different watersheds in east Taiwan. Then, with data from watershed management projects applied in the study areas, the analysis results show that the current completeness ratios are 88% for Meilun Watershed of Hua Lien county and 19% for Chihpen Watershed of Tai Tung county.